The present invention relates to an industrial robot such as a horizontal multijoint robot with an improved wiring/piping system in a robot main body.
As a conventional wiring/piping system in a horizontal multijoint robot, techniques disclosed in Japanese Patent Laid-Open No. 62-68788, Japanese Patent Publication Nos. 63-500505 and 63-36913, Japanese Utility Model Publication No. 63-31912, and the like are known.
More specifically, in a wiring/piping mechanism disclosed in Japanese Patent Laid-Open No. 62-68788, as shown in FIG. 1, wiring/piping lines are connected from a junction box a to a rear portion of a first arm c via a first pipe b, are connected from the first arm c to a second arm e via a second pipe d, are connected from the second arm e to a vertically movable table g, which is vertically movably supported, via a third pipe f, and are finally connected to a finger h attached to the lower end of the vertically movable table g.
In a wiring/piping mechanism disclosed in Japanese Patent Publication No. 63-500505, as shown in FIG. 2, wiring/piping lines are connected from a base i to a second arm e via a first pipe b, are connected from the second arm e, via a second pipe d, to a driving mechanism k which is attached to the distal end of the second arm e so as to vertically move and rotate a vertical arm j, and are finally connected to a finger h attached to the lower end of the vertical arm j.
As another conventional wiring/piping means, a structure shown in FIG. 3 is known. In this structure, wiring/piping lines are connected from a junction box a, via a first pipe b, to a fixing jig m mounted on a first arm c, are connected from the jig m to the upper end of a hollow vertical arm j via a second pipe d, and are then connected to a finger h attached to the lower end of the vertical arm j via the interior of the vertical arm j.
On the other hand, a wiring/piping mechanism disclosed in Japanese Patent Publication No. 63-36913 comprises first and second flexible pipes b and d for supplying a control signal to a driving source of a finger h, and supplying compressed air as a working fluid, as shown in FIG. 4. One end of the first pipe b is connected onto a first arm c which is located on substantially the center of rotation of a second arm e, and the other end thereof is connected to a wiring/piping fixing jig l fixed to a base i. One end of the second pipe d is connected to the upper end of a block k to which a third arm j is vertically movably attached, and the other end thereof is connected to the first arm c which is located on substantially the center of rotation of the second arm e.
In a wiring/piping mechanism disclosed in Japanese Utility Model Publication No. 63-31912, as shown in FIG. 5, wiring/piping lines connected up to a first arm c are connected to a fixing jig n in a spiral pattern m, are connected from the jig n to a fixing jig q fixed to a base i via a U-shaped pipe p, and are then connected from the jig q into the base i in a spiral pattern r.
However, in the prior art shown in FIG. 1, a bundle of wiring/piping lines may be entangled around the finger h upon rotation of the finger h. In particular, when the bundle of wiring/piping lines includes a large number of lines, it is substantially impossible to prevent these lines from being entangled around the finger h. Since the bundle of wiring/piping lines is connected from the vertically movable table g to the second arm e via the third pipe f, is connected from the second arm e to the first arm c via the second pipe d, and is then connected to the junction box a via tho first pipe b, a total of three pipes b, d, and f are required. In this manner, problems causing an increase in cost including connection of wiring/piping lines and working of, e.g., jigs for fixing pipes are posed.
When the first arm c is rotated, the first and second pipes b and d interfere with each other. Connection positions of the second and third pipes d and f to the second arm e are separated far away from the center of rotation of the second arm e, and when the second arm e is rotated, a distance between nuts e1 and e2 for fixing the two ends of the second pipe d is largely changed. As a result, the second pipe d is considerably swung upon rotation of the first arm c.
In the prior art shown in FIG. 2, since the bundle of wiring/piping lines is connected from the second arm e to the driving mechanism k, and is then connected to the finger h, the bundle is entangled around the vertical arm j and the finger h upon vertical movement and pivotal movement of the finger h about the vertical axis. The connection positions of the first and second pipes b and d are separated far away from the center of rotation of the second arm e, and like in the prior art shown in FIG. 1, when the second arm e is rotated, the distance between nuts el and e2 for fixing the two ends of the second pipe d is considerably changed. As a result, the second pipe d is considerably swung upon rotation of the first arm c.
In the prior art shown in FIG. 3, since the bundle of wiring/piping lines from the finger h extends through the vertical arm j, they can be prevented from being entangled around the vertical arm j upon vertical movement and pivotal movement of the vertical arm j. However, since the bundle of wiring/piping lines extending from the upper portion of the vertical arm j is connected to the fixing jig m on the first arm c via the second pipe d, the bundle of wiring/piping lines in the second pipe d receives excessive torsion since they absorb torsion caused by vertical movement and pivotal movement of the vertical arm j and pivotal movement of the second arm e, thus posing a large problem on the durability and reliability of the wiring/piping lines.
The durability of a bundle of wiring/piping lines will be examined below. A bundle used here is a robot cable, and is obtained by twisting and bundling lines having cores smaller than those in a normal cable. As a result, this bundle has high flexibility, and has durability against bending and torsion ten times or more than a normal cord.
Durability tests are conducted in such a manner that a cable n is bent at 90.degree. to the right and left at a rate of 60 times/minute to have a bending radius of 17.5 mm. As a result, it was demonstrated that the cable was disconnected after about two million times. Although a cable arranged in an actual robot does not suffer from such a severe condition, i.e., a bending radius of 17.5 mm, torsion as a factor for impairing the durability of the cable is mainly caused by bending, and the number of times of bending reaches ten thousands times/day depending on a use state of a robot. Therefore, the wiring method in the robot must be sufficiently examined so as not to apply a stress on a cable.
In the prior art shown in FIG. 4, since the wiring/piping fixing jig l is offset from the center of rotation of the first arm c, when the first arm c is rotated, the distance between fixing nuts b1 and b2 of the first pipe b is largely changed. For this reason, when the distance between the nuts is decreased, a height H of the first pipe b is increased, as shown in FIG. 7A, and the first pipe b is inclined upon rotation of the first arm c. As a result, a large load caused by the inclined pipe b acts on the nuts b1 and b2. On the other hand, when the distance between the nuts is increased, the height of the first pipe b is decreased, as shown in FIG. 7B, and a large load also acts on the nuts b1 and b2. In this manner, the first pipe b may be undesirably disengaged at the nuts b1 and b2 at its two ends.
In particular, since the degree of freedom of the finger h is increased, and the number of wiring/piping lines to the finger h tends to be increased in recent years, the number of wiring/piping lines extending through the first pipe b may exceed 10 if they include a wiring line for a control signal to an arm driving motor. For this reason, the inclination of the first pipe b when the first arm c is turned is further increased, and a thick pipe member is used. Therefore, in order to store a large number of wiring/piping lines, and to maintain these lines in an upright state, the rigidity of the pipe member must be increased, and a load acting on the nuts b1 and b2 is increased accordingly.
In the conventional wiring/piping system, since the second pipe d is connected to the upper portion of the first arm c, wiring/piping lines extending through the second pipe d must absorb torsion caused upon rotation of the second arm e, and torsion caused upon rotation and vertical movement of the third arm j, thus considerably impairing the durability and reliability of the wiring/piping lines.
Furthermore, in the prior art shown in FIG. 5, a wiring line o extending from the first arm c passes through the interior of the U-shaped pipe p in the spiral pattern m, and is then connected to the base g in the spiral pattern r. As a result, even when the first arm c is rotated, torsion of wiring lines caused by this rotation is absorbed by the spiral portions m and r, and the durability of the wiring lines and the like can be guaranteed. However, since the two spiral wiring portions are required, and the U-shaped pipe p is arranged therebetween, the numbers of steps in the manufacture of the fixing jigs, and in assembling and connection of wiring lines are increased, resulting in an increase in cost. In addition, such a structure makes maintenance difficult.